The objective of this program is to identify and functionally characterize neurogenic genes that are required for CNS development. Given the high degree of conservation observed in basic mechanisms utilized by all metazoans, our search for these genes was initiated in the fruit fly (Drosophila melanogaster) where developmental information is more accessible for study. Using classical genetic, molecular biology and transgenic techniques, we have continued to study the function of castor, a novel Zinc finger gene required for proper CNS neuroblast development and pollux, a novel cell-adhesion protein encoding gene also expressed in the developing CNS. We hypothesize that the castor protein functions as a DNA-binding transcription factor required for the regulation of genes involved in neuroblast development. Consistent with its proposed role, our recent studies have shown that the castor encodes a nuclear protein that complexes with DNA in vivo. To test our hypothesis, we are currently characterizing genomic DNA clones that contain in vivo castor protein DNA-binding sites to identify genes that may be regulated by castor. We have also pursued the characterization of cognate genes by first cloning castor and pollux cognates from other dipteran species. Information obtained from these comparisons will aid in our identifying mammalian cognates. Protein data bank searches have revealed that pollux is related to three human proteins. Recent studies on pollux have shown that it encodes a membrane associated protein that can serve as a ligand for RGD-binding integrins. Analysis of pollux mutant alleles revealed that it is required for proper trachea function. During our studies on pollux, we serendipitously observed high levels of male homosexual behavior in transgenic flies. Genetic and mutant analysis of these lines demonstrated that the behavior is triggered by the hyper or ectopic expression of the transgene vector's selectable eye marker, the mini-white gene. We have also continued our functional analysis of the murine homeobox gene A5. Ectopic expression of A5 in transgenic mice correlates with the apparent repression of a hepatocyte nuclear transcription factor (HNF-3b) in adult tissues. We are now assessing if in utero ectopic A5 expression modulates HNF-3b expression during development.